I realize that the discussion of what defines open source is off-topic, but as you've left your original confusing comment I'll repeat:

APE, despite the availability of it's source code, is *not* open source (as defined by the OSI and, imho, as generally accepted by programmers of all kinds).

Real world effects of this are that certain influential Linux distributions will not include the code (Debian for one) which limits it's acceptance and use in the Linux community as does the fact that no open source (per OSI) programs can build upon the code unless they ask for it to be relicensed (which they have previously, and been turned down).

Also, each business that wishes to use the code will need to negotiate with the author the exact terms of use in advance, rather than deal with a known license that is in common use. This (imho) limits the chance of it being adopted by businesses.

Other miscelleaneous problems include the legal limbo if the original author dies or just becomes difficult to contact etc.

The above is an on-topic comment as far as APE vs. FLAC is concerned as FLAC is under an OSI approved licence (i.e. what I would call "open source") and for some people this is an important distinction and reason for choosing one over the other. And not *all* of these people are zealots or just the general kind of idiots you commonly find cheerleading for Ogg Vorbis.